1. Field of the Invention
The present invention relates generally to electronic signal processing circuitry. In particular, the present invention to an electronics circuit for the determining the position of incident light on a position sensing detector.
2. Description of the Prior Art
Position sensing detectors are being utilized to make distance measurements of underwater surfaces for the purpose of three dimensional mapping of the underwater surface. Typically, optical triangulation techniques are used to measure the measure and thus map the underwater surface. A collimated beam of laser light is focused by motorized beam guidance system on the underwater surface or like surface to be measured. The light beam is scattered diffusely from the undersurface surface and then collected by a lens which focuses it to a point on the surface of the position sensing detector. The position the light is incident on the underwater surface is used in conjunction with the position of a mirror of the guidance system to derive the distance to the underwater surface. As the distance from the light source to the underwater surface changes, the position the light is incident on the position sensing detector will be displaced as a function of the change in distance of the light source from the underwater surface.
The position sensing detector in response to the position the light is incident on its surface provides a pair of photocurrent output signals. The photocurrent output signals are converted to first and second voltage signals and amplified by an operational amplifier/feedback circuit. The amplified voltage signals are next processed by a sum and difference circuit which provides sum and difference signals for the amplified voltage signals. The sum and difference signals are supplied to an analog voltage divider which divides the difference signal by the sum signal and provides an analog output signal. The resulting analog output signal indicates the light is incident on the position sensing detector.
The accurate detection of the position of the reflected light beam on the position sensing detector is of concern to an individual mapping an underwater or like surface, since inaccuracies may occur in the mapping of an underwater surface using conventional signal processing techniques such as the technique previously discussed.
In particular, position sensing detectors generally provide a "dark current" or noise whose magnitude is of concern when compared to the magnitude of the light position photocurrents provided by the position sensing detector especially in underwater and like environments where the reflected light beam is very weak due to weak target reflectivity as well as spherical losses which occur during the mapping process. Further, when measurements are made in a deep underwater environment the intensity of the reflected light may vary significantly which necessitates the use of variable gain amplification of the signals provided by the position sensing detector to provide for voltage levels which are acceptable for analog-to-digital converters and other position calculation circuitry.
In view of the foregoing, it is an object of the present to provide an electronics circuit which allows for the accurate calculation of the position of light incident on the surface of a position sensing detector.
It is another object of the present invention to provide an electronics circuit which removes dark current from the photocurrent output signals provided by position sensing circuit thereby allowing for the accurate calculation of the position of light incident on the surface of the position sensing detector.
It is still another object of the present invention to provide an electronics circuit which provides a variable gain amplification factor to allow for an accurate calculation to the position of light incident on the surface of the position sensing detector.
Various other advantages and objects of the present invention will become apparent to those skilled in the art as a more detailed description of the invention is set forth below.